This invention relates to a method of preparing a transition metal catalyst for use in the synthesis of ammonia and to the novel transition metal catalyst obtained by practice of the invention.
In the Haber-Bosch process, nitrogen and hydrogen gas are reacted in the presence of an iron catalyst to produce ammonia, according to reaction (1). EQU 1/2N.sub.2.sup.(g) + 3/2H.sub.2.sup.(g) .revreaction. NH.sub.3 (g) (1)
The forward reaction, which is exothermic, is increasingly favored as the temperature is reduced. The yield is also increased by increasing the pressure. Therefore, it is desirable to perform the reaction at low temperatures and high pressures.
In common practice, the reaction is performed in a high pressure vessel wherein the catalyst is provided in a basket such as to allow the reaction gases to percolate through the catalyst. In order to maintain the reaction temperature constant, the catalyst bed has to be cooled.
The catalyst most commonly used in the industrial production of ammonia is composed predominantly of magnetite (FeO.Fe.sub.2 O.sub.3) wherein other oxides may be present in trace amounts. Promotors are usually added to increase the activity of the catalyst. These compounds are oxides, isomorphous with FeO or Fe.sub.2 O.sub.3, bearing a metal similar in molecular volume to iron; for example, MnO, MgO, ZnO, Cr.sub.2 O.sub.3, in combination with K.sub.2 O and Al.sub.2 O.sub.3. Prior to use, the iron catalyst must be activated by reducing it to metallic iron, usually by heating under a stream of hydrogen gas. During this process, cavities are formed in the original oxide lattice resulting in an increase in the surface area. The surface area of such a catalyst is usually in the range of 4-15 m.sup.2 /g of catalyst. The promoters do not undergo reduction in this process. An iron catalyst produces a yield of approximately 12% ammonia under typical reaction conditions of about 525.degree. C. and 150 atmospheres at a space velocity of 20,000 v/v.